1. Field of the Invention
The invention relates to a method for manufacturing hollow spaces in metallic workpieces, especially in fuel injectors for diesel engines with at least one main bore and at least one supply bore, especially for the fuel supply, wherein at least one electrode is introduced into the main bore and the hollow space and/or the connection to the supply bore is formed by means of an electrolytic erosion process.
2. Description of the Related Art
In a known manufacturing process for fuel injectors, a main bore is produced in the workpiece. Subsequently, the manufacture of the supply bore takes place. The nominal diameter of the supply bore of the fuel injectors for diesel engines with minimal power output is often less than 1 millimeter. During the manufacturing process, contaminants such as oil residues from drilling or small metal shavings are introduced into the supply bore and into the main bore. For an electrolytic erosion process, it is necessary that the main bore and the supply bore are free of contaminants because the latter form an insulation layer on the metal surface so that during the electrolytic erosion process a non-uniform erosion of metal takes place.
In order to prevent these negative results, the workpiece, after producing the bores, is freed of contaminants by time-intensive and cost-intensive washing processes. Due to the often very minimal diameter of the supply bore, the effect of capillary forces is especially great. Oil residues can be removed only by a very complex washing process at high-pressure and by employing expensive detergents. After the washing processes, the supply bore is then sealed to the exterior and the actual electrolytic erosion process begins. A voltage is applied to the electrode positioned in the main bore. The electrolyte liquid is then supplied via the electrode, metal is removed, and the electrolyte liquid is then removed completely through the main bore. This process is continued until the hollow space has reached the desired size and a connection between the main bore and the supply bore is present.
It is an object of the invention to provide a method with which the use of an additional washing process is eliminated.
The object of the invention is solved in that the supply bore is flushed at least temporarily with the electrolyte. The electrolyte liquid reaches the main bore through the electrode or by flowing past it. Because of the high flow velocity, the electrolyte liquid removes contaminants from the surface. Once the hollow space formation has reached the supply bore, the electrolyte liquid flows through the supply bore to the exterior. Because of the flow-through amount and the rate of flow, oil residues and other contaminants are flushed out. In order for the erosion of metal in the supply bore not to surpass a certain amount, the flow-through can be interrupted by closing the supply bore.
This new method makes it possible to save additional washing processes which incur considerable costs. Firstly, an enormous amount of time is saved because the assembly and the retooling required for the washing processes can be eliminated.
When the supply bore is kept open for a longer period of time, an asymmetric formation of the hollow space results because the entire flow pattern on which the shape of the hollow space depends is changed. A portion of the electrolyte liquid is removed through the supply bore so that the erosion at the side opposite the supply bore is slowed. The formation of asymmetric hollow spaces is advantageous for many applications. When it is desired to form the hollow space symmetrically, it is recommended to close the supply bore toward the end of the process so that a back formation of the asymmetry results. This effect can be explained in that the less strongly eroded locations are again more strongly eroded by the proximity to the electrode when the supply bore is closed.
According to one embodiment of the invention, the supply bore is flushed from the interior to the exterior. When the supply bore is flushed in this direction, not only are contaminants very effectively removed from the bore, but a surprising side effect results. The junction edge of the supply bore adjoining the hollow space is rounded by the electrolyte liquid flowing past it and the entire junction area is smoothed. This effect is the result of the high flow velocity and the eroding properties of the electrolyte liquid. A rounded and smoothed edge has the advantage that the entire workpiece is essentially more pressure-stable. This is important with respect to the future because the development of diesel engines continues to proceed in the direction of higher injection pressure of up to several thousand bar. This is thought to achieve an improved combustion of the fuel.
According to a further advantageous embodiment of the invention the electrolyte liquid is removed through the electrode and/or Introduced through the electrode. This embodiment of the invention ensures a uniform flow pattern which is of utmost importance for a fast and uniform formation of the hollow space. In order for the supply and removal of the electrolyte liquid to be carried out in an optimal way, the electrode is formed as a tube with beaded edges. The electrolyte liquid can thus pass unimpeded through the electrode.
In order to prevent that metal is removed at undesirable locations of the workpiece, these locations are protected by insulators. Accordingly, no electrolyte liquid can reach these locations, the workpiece remains thus undamaged there and maintains its original shape.
Contaminants in the electrolyte liquid affect the erosion behavior negatively. Accordingly, it is provided according to an especially advantageous embodiment that the electrolyte liquid is freed of contaminants. For example, oil and foam separators are employed.
In order to clearly structure the method and to separate individual processes from one another, according to a further advantageous embodiment of the invention it is provided that the manufacture of the workpiece is carried out in several partial steps.
According to an advantageous embodiment of the invention, it is provided that the electrolyte liquid flows through at least one opening in the insulator. With this measure an unimpeded removal or supply of the electrolyte liquid is ensured.
According to a further very advantageous embodiment of the invention, it is provided that the electrolyte liquid flows through at least one channel below the supply bore. This channel can be integrated in the insulator so that the electrolyte liquid can exit, for example, laterally. It is also conceivable that the channel is not integrated into the insulator. In this way, insulation material can be saved.
The invention will be explained in more detail with the aid of the drawings illustrating embodiments of the invention.